The performance of surgery requires that a retractor hold out of the way all tissues down to the actual surgical site. When performing a posterior approach to the thoracic or lumbar spine, it is necessary to retract very large and strong paraspinal musculature masses. Because of the differences in the size of patients and the relative mass of the muscles along various portions of the spine, it would be necessary to have a series of retractors with permanently attached blades or series of blades that could be attached or removed as needed from a basic blade-holding retractor frame. However, to keep the retractor blades from ejecting from the wound under the pressures generated by the muscle retraction, it is necessary to have the blades both diverge from the center line distally, and further to have large sharp teeth at a right angle to the longitudinal access of the blades so as to lock the blade tips beneath the muscle masses.
If the blades are divergent distally and in addition are splayed, then even with the retractor fully closed, the blades, if pre-attached to the retractor, would not be insertable into the wound as the outside of the tips of the blades would be further apart than the wound is wide. Therefore, retractors having pre-fixed blades must compromise the blade contour to fit in the wound by having less divergent and less angulated blades. Such a configuration significantly diminishing the ability to function as a deep wound retractor. Thus, spinal retractors with attachable blades have been devised.
At present, there are essentially two types of large spinal retractors with attachable and removable blades. Such retractors and blades are shown in FIGS. 10 and 11.
The first type (shown in FIG. 11) consists of a blade with a rectangular shaped opening at the top into which the retractor arms can be slid to hold the blade. While this does allow the blade to be inserted into the wound first and the retractor arms then attached, there can be great difficulty in attaching the blades to the retractor arms as both blades must be engaged simultaneously which requires that the blades and the arms of the retractor be opened to exactly the same width. Further, the blades must be parallel to each other and to the retractor and at the same time must protrude from the wound to exactly the same height. Further, the blades must be absolutely perpendicular to the spine, and not be rotated. Achieving all of these conditions at the same time can be quite difficult and time consuming.
There is also a retractor set which uses a rectangular open box-like attachment method, where the blades are strips of metal of similar widths and different lengths such that a series of strips are attached to each arm until a whole blade is essentially constructed, contoured to the particular patient. However, since the blades are attached to the retractor prior to insertion, the blades cannot be optimally divergent thereby defeating at least one of the two major advantages sought to be obtained from the use of the attachable blades.
The second type of large spinal retractor currently in use (FIG. 10) utilizes a set of attachment posts protruding from the retractor arms which then engage a series of corresponding holes on the top surface of the blades. However, when these blades are placed within the wound first and then an attempt is made to attach the retractor, there is considerable difficulty in aligning the blades and achieving the necessary three dimensional parallelism so as to attach the blades to the retractor. Furthermore, the exposed pegs and locking mechanism pose a threat to the surgeon as it is possible to rupture a glove on the exposed mechanism.